Circuit arrangement for producing a direct voltage by means of a resistance element having a non-linear symmetrical current-voltage characteristic



Sept. 6, 1966 A BQEKHQRST I 3,271,617

CIRCUIT ARRANGEMENT FOR P RODUGING A DIRECT VOLTAGE BY MEANS OF A RESISTANCE ELEMENT HAVING A NON-LINEAR SYMMETRICAL CURRENT-VOLTAGE CHARACTERISTIC Filed Feb. 26, 1962 2 Sheets-Sheet 1 72 VVDR --Vnet 26 F e Fl 6 5 lNVENTOR ANTONIUS BDEKHORST BYE/1M AG EN Dept. 6, 1966 BOEKHQRST 3,271,617

CIRCUIT ARRANGEMENT FOR PRODUCING A DIRECT VOLTAGE BY MEANS OF A RESISTANCE ELEMENT HAVING A NON-LINEAR SYMMETRICAL CURRENT-VOLTAGE CHARACTERISTIC Filed Feb. 26, 1962 2 Sheets-Sheet 2 INVENTOR ANTONIUS B OEKHO RST Q M/ L AGENT United States Patent 3,271,617 CIRCUIT ARRANGEMENT FQR PRODUCING A DIRECT VGLTAGE BY MEANS OF A RESIST- ANCE ELEMENT HAVING A NDN-LINEAR SYM- SIEICAL CURRENT-VOLTAGE CHARACTER- Antonins Boekhorst, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York,

N.Y., a corporation of Delaware Filed Feb. 26, 1962, Ser. No. 176,492 Claims priority, application Netherlands, Apr. 13, 1961, 263,600/ 61 12 Claims. (Cl. 31527) This invention relates to circuit arrangements for producing a direct voltage by means of a resistance element having a non-linear symmetrical current-voltage characteristic and a capacitor connected in series with it, an asymmetrical alternating voltage being applied to this series-combination and the direct voltage produced being retained by the capacitor.

In conventional circuit arrangements the asymmetrical voltage applied to the element having the non-linear asymmetrical current-voltage characteristic was invaribly derived directly from .a special circuit. Thus, for example, in US. Patent No. 2,628,326, the asymmetrical voltage is the pulsed voltage produced in a line-deflection circuit.

However, if an asymmetrical voltage source is not available, a direct voltage may still be obtained with such a resistance element by following the teachings of the invention. In accordance with the invention the circuit is characterized in that the asymmetrical alternating voltage is produced by applying a symmetrical alternating voltage to the series combination itself and a bias voltage to the resistance element.

In order that the invention may be readily carried into effect, several embodiments thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 shows a rectifying circuit for producing a stabilized direct voltage;

FIGURE 2 shows a characteristic curve illustrating the relationship between the total direct voltage V across the series-combination of the ohmic resistor and the voltagedependent resistor shown in FIGURE 2a and the direct voltage V across the voltage-dependent resistor for an increasing supply voltage V FIGURE 2a shows the total direct voltage V across the series combination of the ohmic resistor and the voltagedependent resistor and the direct voltage V across the voltage-dependent resistor;

FIGURE 3 serves to explain, in combination with the characteristic curve of FIGURE 2, the operation of the circuit shown in FIGURE 1;

FIGURE 4 shows the output voltage V, of the circuit in FIGURE 1 as a function of the supply voltage V and FIGURE 5 shows a particular embodiment of a circuit arrangement according to the invention.

In FIGURE 1 the primary winding of a transformer 1 is connected to the supply voltage V A conventional rectifying circuit comprising a diode 2 and a smoothing network constituted by a choke coil 3 and two smoothing capacitors 4 and 5 is connected to the secondary winding of transformer 1. A direct voltage V is thus set up across the second capacitor 5, which is a positive direct voltage in view of the mode of connection of diode 2 shown in FIGURE 1. As a matter of fact, a negative direct voltage may be developed across capacitor 5 by reversing the connections of diode 2.

ice

A second rectifying circuit comprising a voltage-dependent resistor 7 and a capacitor 8 is connected to a tapping 6 on the secondary winding of transformer 1. As is well known, a voltage-dependent resistor can act as a rectifying circuit only if an asymmetrical alternating voltage is applied to it. According to the invention, the asymmetry is obtained by applying a biasing potential to voltage-dependent resistor 7 through an ohmic resistor 9, so that it becomes possible to rectify the alternating voltage derived from tapping 6. Since an alternating voltage having a sinusoidal waveform is applied to the primary winding of transformer 1, the alternating voltage between tapping 6 and ground is also sinusoidal and hence symmetrical relative to ground potential.

Due to the biasing potential applied to resistor 7, it is possible to derive a voltage from the circuit arrangement of FIGURE 1 which is increasing, or decreasing, or constant with increasing supply voltage V This may be explained as follows:

Since substantially no direct voltage appears across the portion of the secondary winding of transformer 1 located between tapping 6 and ground, the direct voltage V developed across capacitor 5 also appears across the series combination of ohmic resistor 9 and voltage-dependent resistor 7. This series combination and the direct voltage V applied thereto is shown for the sake of convenience in FIGURE 2a, in which the direct voltage across voltage-dependent resistor 7 is indicated by V The total voltage V and the voltage V are plotted as a function of the supply voltage V in FIGURE 2. The total voltage V increases proportionally to V whereas the voltage V as a result of the non-linear characteristic of voltage-dependent resistor 7, increases to a lesser and lesser extent with increasing supply voltage V In the foregoing discussion, voltage V has been assumed to be positive so that the junction of voltage-dependent resistor 7 and capacitor 8 is positive relative to the junction of voltage-dependent resistor 7 and tapping 6 or, in other words, tapping 6 is negative relative to the junction of resistor 7 and capacitor 8. As previously mentioned, no direct voltage is developed across the portion of the secondary winding located between tapping 6 and ground. Therefore, the direct voltage V is also set up as a positive direct voltage across capacitor 8, i.e. cs vna- The biasing potential V provides that the alternating voltage across voltage-dependent resistor 7, produced by the alternating voltage derived from tapping 6, does not fluctuate symmetrically about ground potential, as would be the case without a bias voltage. The alternating voltage at tapping 6 must, for example, first have assumed a positive voltage equal to the voltage V before the voltage at the junction of capacitor 8 and voltage-dependent resistor 7 becomes zero.

This is clarified more fully in FIGURE 3, in which curve 10 represents the non-linear current-voltage characteristic of voltage-dependent resistor 7. In the absence of biasing potential across voltage-dependent resistor 7, the alternating voltage would fluctuate about the vertical axis in FIGURE 3 which represents ground potential. The mean value of the current through capacitor 8 (the capacitance of capacitor 8 is such that, for the frequency of the alternating voltage used, the impedance of this capacitor is low relative to each possible ohmic value of voltage-dependent resistor 7 so that substantially no alternating voltage is developed across capacitor 8) is then zero so that on the average no load is supplied to capacitor 8 by the alternating current. Consequently, a recti fying action is in this case out of the question.

If, however, a biasing potential is applied to voltage-dc pendent resistor 7, the alternating voltage no longer fiucage V having an amplitude thus fluctuates about a value V represented by line 11. Due to the biasing potential V alone, a current I would flow through voltage-dependent resistor '1, but the applied alternatingvoltage V also causes an alternating current I to flow through it.

As may clearly be seen from FIGURE 3, the means current I of the alternating current 1 is negative, which means that on the average a negative charge is supplied to capacitor 8. In other words, due to the application of the biasing potential V =V the alternating voltage V of amplitude can provide capacitor 8 with a negative voltage V caused by the negative mean current I The negative voltage V causes a decrease in the positive direct voltage V which already exists across the capacitor.

The fact that the voltage V must in practice be subtracted from the voltage V may also be recognized as follows. If the alternating voltage at tapping 6 goes positive with respect to ground, the alternating current tends to flo'w from tapping 6 through resistance element 7 and capacitor 8 to ground. This is a positive-going current which supplies, as it were, positive charge to capacitor 8.

The current I resulting from the direct voltage V is directed from the choke coil 3 via ohmic resistor 9, voltage-dependent resistor 7 and tapping 6 to ground. The current I and the positive portion of the alternating cur- 'rent I are thus oppositely directed in voltage-dependent resistor 7 and counteract each other.

When the alternating voltage at tapping 6 goes negative with respect to ground, the alternating current has the same sense as the current I in voltage-dependent resistor 7, so that the current I and the negative portion of the alternating current I support each other. The nega tive portion of the alternating current is thus greater than its positive portion so that on the average negative charge is supplied. The positive charge resulting from the biasing potential V g is thus decreased.

From the foregoing it follows that the operation remains unchanged if capacitor 8 and voltage-dependent resistor 7 are interchanged. True, the positive portion of the alternating current through the series-combination of capaictor 8 and resistance element 7 is in this case predominant, but this still tends to decrease the charge caused by the biasing potential V However, as may be seen from FIGURE 2, as long as the voltage V is comparatively low, the voltage V across voltage-dependent resistor 7 increases to a greater extent with increasing V than does the voltage V-V across ohmic resistor 9. From this it follows that the biasing potential V increases more rapidly with a low increasing V and hence also the positive potential V V across capacitor 8, than the negative voltage V obtained by rectification of the alternating voltage between tapping 6 and ground by means of voltage-de pendent resistor 7 and capacitor 8, since a certain bias ing potential V must first be built up before rectifica' tion by the said portion of the circuit is possible.

However, as V increases further, V and hence V g, increases to a lesser and lesser extent (see FIGURE 2), but the rectified voltage V increases to a greater and greater extent. This may be shown by reference to the alternating voltages V V and V shown in FIG URE 3, the amplitudes V and V of which, together with the currents caused by them, may be calculated in the simplest way with reference to a numerical example. However, it will be evident that this numerical example is given only by way of example and that the operation of the circuit arrangement is similar also with different proportioning of the component parts.

The voltage across voltage-dependent resistor 7 is given by V =CI,B, where [3:02 and C=20O volts/ amp. for i=1 ampere. Resistor 9 has a value of K ohms.

Assuming the tapping 6 to be a center tap, the amplitude of the alternating voltage across it is half the amplitude of the alternating voltage across the whole secondary winding of transformer 1. It is also assumed that peak rectification by means of diode 2 and the associated smoothing network occurs. With these assumptions it is possible to calculate the values of current and voltage given in the table below.

TABLE In In volts mamp.

V l 'r V01 I01 25. O 12. 5 23. O 0. O2 02 02 32.6 m 3 -27. 6 0. 05 if? V0: 03

The values given in the table above, neglecting the alternating-voltage drop across the large capacitor 8, are plotted in FIGURE 3. It appears that the alternating current I caused by an alternating voltage V having an amplitude l acquires a minimum negative value of 0.01 mamp. and a maximum negative value of O.23 ma. The corresponding mean current I =0.09 mamp. The rec tifying action may also be explained from the fact that |I [I If resistance element 7 exhibited a linear characteristic curve, this formula would have been |I ]=[I and rectification would be out of the question.

The alternating current I caused by an alternating voltage V having an amplitude V} has a minimum negative value of 0.01 mamp. and a maximum negative value of 0.53 mamp. The corresponding mean current having an amplitude V of 20.8 volts follows from the table. The resulting alternating current I has a minimum value of about 0.01 mamp., a maximum value of 1.27 mamp. and a mean current I of 0.4 mamp. Hence in this case also ]I ]I The further increase from 27.6 volts (being V to 31.7 volts (being V thus gives an increase in the voltage V g by a factor of 77 constituted by the display tube, and with regard to variations in the supply voltage. Voltage-dependent resistor 21 with its associated elements is responsible for the stabilization with regard to variations in the high voltage load. The stabilization for variations in the supply voltage is determined substantially by the circuit according to the invention and otherwise by voltage-dependent resistor 21 with its associated circuit elements. Although the circuit arrangement shown in FIGURE has been described for a line-deflection circuit, it will be evident that the circuit according to the invention may also be incorporated in any other circuit arrangement requiring a negative or positive voltage for stabilizing purposes. The circuit of FIGURE 1 may also be used directly if a constant direct voltage is required which in this case may be derived from the tapping 13 in FIGURE 1.

It is not necessary that resistance element 7, having the non-linear current-voltage characteristic, be a voltagedependent resistor. A resistance element having a strong- 1y negative temperature coefficient could also be used for this purpose. In this case, the frequency of the alternating voltage employed must then be low enough so that the resistors of negative temperature coefiicient, which is usually slow acting, can follow the alternating voltage.

What is claimed is:

1. A circuit for producing a direct voltage for a load device comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, a source of a symmetrical alternating voltage, means serially connecting said source, resistance element and capacitor, means providing a direct voltage bias to said resistance element whereby a direct voltage is produced across said capacitor, applying at least a portion of said produced direct voltage to said load device.

2. A circuit for producing a direct voltage comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, a source of a symmetrical alternating voltage, means serially connecting said resistance element and capacitor to said source of alternating voltage, a linear resistor, a source of a direct voltage, means connecting one end of said linear resistor to one end of said resistance element, and means applying said direct voltage to the series combination of 'said resistance element and said linear resistor, whereby a direct voltage is produced across said capacitor.

3. A circuit for producing a direct voltage comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, 2. source of a symmetrical alternating voltage, means serially connecting said resistance element and capacitor to said source of alternating voltage, a source of direct voltage having an amplitude proportional to the amplitude of said alternating voltage, a linear resistor, means connecting one end of said lineal resistor to one end of said resistance element, and means applying said direct voltage to the series combination of said resistance element and linear resistor, whereby a direct voltage is produced across said capacitor.

4. The circuit of claim 3, wherein said linear resistor comprises first and second series connected resistors with one end of said first resistor being connected to said resistance element, comprising means for obtaining an output voltage from the series circuit of said resistance element and said first resistor, and the values of said first and second resistors are determined by the expression:

wherein AV is an incremental change of said direct voltage which accompanies an incremental change AV in the opposite direction of the voltage across said capacitor, and R and R are the resistances of said first and second resistors, whereby said output voltage is constant.

5. A circuit for producing a direct voltage comprising a transformer having a primary winding and a tapped secondary winding, a source of alternating voltage connected to said primary winding, said tapped winding having first and second ends, a series circuit of rectifier means, a tapped linear resistor and a capacitor connected in that order between said first and second ends of said secondary winding, a resistor element having symmetrical non-linear current-voltage characteristics connected between the tap of said secondary winding and the junction of said capacitor and linear resistor, and means for obtaining an output voltage between said second end of said secondary winding and the tap of said linear resister.

6. A line deflection circuit for a television receiver, comprising an amplifier device having a control electrode and an output electrode, a source of a control voltage for periodically releasing said device connected to said control electrode, a line output transformer, a line deflecting coil, a series booster diode, means coupling said deflection coil to said transformer, means connecting the cathode of said diode to said coil, a series booster capacitor connected in series with said coil, means connecting said output electrode to said coil, a source of direct voltage connected to the anode of said diode, and means for stabilizing the current through said amplifier device on variation of said direct voltage comprising a source of alternating voltage which varies in amplitude proportional to variations of said direct voltage, a resistance element having non-linear symmetrical current-voltage characteristics, a first capacitor connected .in series with said element, means applying said alternating voltage to the series combination of said resistance element and first capacitor, linear resistor means connected between said booster capacitor and said resistance element to provide a bias for said element, and means applying the voltage across said first capacitor to said control electrode, whereby the voltage across said first capacitor decreases with increases of said alternating voltage above a predetermined level.

7. The circuit of claim 6, in which said amplifier device is an electron discharge device having a control grid, a screen grid and anode, said control electrode being said control grid and said output electrode being said anode, comprising means for applying said direct voltage to said screen electrode.

8. A circuit for producing a direct voltage comprising a resistance element having a non-linear symmetrical current-voltage characteristic curve, a capacitor, a source of a symmetrical alternating voltage of a given amplitude, means connecting said resistance element and said capacitor in series circuit with said alternating voltage source to form a closed current path, means providing a direct voltage to said resistance element of a magnitude to bias said resistance element to operate over the non linear region of said characteristic curve for said given amplitude of the alternating voltage source whereby a direct voltage is produced across said capacitor, and output circuit means coupled to a portion of said circuit in cluding said capacitor for supplying a direct voltage output.

9. A circuit for producing a direct voltage comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, a source of a symmetrical alternating volt-age of a given amplitude, means connecting said resistance element and said capacitor in series circuit with said alternating voltage source, means providing a direct voltage bias to said resistance element of substantial amplitude relative to said given duce a net mean current flow to said capacitor which charges said capacitor in a direction to oppose said given polarity, and output circuit means coupled to said capacitor for supplying a direct voltage output.

while the increase in the rectifying voltage V is proportional to a factor of From this it may be concluded that the resulting voltage V =V V has decreased to a greater extent with the increase in the voltage V from 32.6 volts to 41.7 volts than with the increase from 25 volts to 326 volts.

From the foregoing it follows that the resulting voltage V across capacitor 8 as a function of the supply voltage V on the primary side of transformer 1, has the waveform shown by curve 12 in FIGURE 4.

The ultimate output voltage V may be derived from the tapping 13 on resistor 9. If the various elements of the circuit arrangement of FIGURE 1 are chosen so that the nominal supply voltage V, corresponds to a voltage V which lies on the negative sloping region of curve 12, it will be evident that, with a correct position of tapping 13, the voltage V remains constant if the supply voltage V varies, since an increase in the voltage V results in a decrease in the voltage V and conversely.

The correct position of tapping 13 may be calculated as follows.

If the portion of resistor 9 located between tapping 13 and capacitor 8 has an ohmic value of R ohms and the other portion has an ohmic value of R ohms, the derived direct voltage V may be written as follows:

If the voltage V increases by an amount AV, the voltage V decreases by an amount AV The variation AV in the derived voltage V may thus be written as follows:

R AVR AV,

From this it follows that AV=0 if R AV=R AV or i= AV R By :proportioming the resistor 9 so that its ohmic value is low relative to the value of resistance element 7 tor a comparatively low direct voltage V, but high with respect thereto tor a comparatively high voltage V, the declined branch of curve 1-2 in a large range is a straight line upon varying mains voltage V Consequently, the relation AV/AV may be regarded as substantially constant over the said range so that the condition found in Equation 1 may be fulfilled in this range.

If the ratio between the resistance portion (R of resistor '9, located between tapping '13 and capacitor 8, and the resistance portion (R located between tapping 13 and choke coil 3 is equal tothe ratio between the voltage variation AV of the voltage V and the voltage variation AV of the voltage V then AV is zero over the said range. In other words, in this case the derived direct voltage V is constant over .the said range.

Tapping 13 may also be chosen so that the voltage V' either decreases with increasing supply voltage (tapping 16 closer to the junction of resistor 9 and capacitor 8) or increases with increasing supply voltage (tapping 13 closer to the junction of resistor 9 and choke coil 3).

-It will be evident that a resulting negative voltage V having a waveform similar to that shown by curve 12 may be obtained by reversing the connections of diode 2.

A possible application of a circuit according to the invention is shown in FIGURE 5. This application relates to the stabilization of a line-deflection circuit in a television receiver. The line-deflection circuit itself comprises an output tube 14, a series-booster diode 15, a lineoutput transformer 16, a line-deflection coil 17, a capaci tor 18 associated with the series-booster diode circuit and a high-voltage rectifier 19. A control voltage 20 is applied to the control grid of tube '14, resulting in a sawtooth current flowing through deflection coil '17 and a pulsed voltage being developed across this coil during the fly-back stroke of the sawtooth current. The pulsed voltage, which in itself may be regarded as an asymmetrical voltage, is rectified in known manner by means of a further voltage-dependent resistor 21. To this end the pulsed voltage is applied to voltage-dependent resistor 21 through the parallel combination of a capacitor 22 and a resistor 23. A negative direct voltage is thus developed which is applied to the control grid of tube 14 via a grid leak resistor 24.

The portion of the circuit including the voltage-dependent resistor 21, resistor 23 and capacitor 22 for producing the negative control-grid voltage has a certain stabilizing action for variations in the high Voltage load on the line-deflection circuit and for variations in the supply voltage +V (which is likewise derived from the supply voltage V by rectification). However, this stabilizing action is insufiicient to compensate for variations in the supply voltage V This is attributable to the fact that a variation in supply voltage exerts its influence upon the line-deflection circuit not only through the varying voltage across capacitor '18, but to an even greater extent via the screengrid voltage V of tube 14, since the object of stabilizing is to keep constant the anode peak current of the tube 14. Consequently, the mean anode current and also the mean screen-grid current are maintained substantially constant. However, a constant screen-grid current implies a constant voltage drop across screen-grid resistor 25. If, for example, the supply voltage V increases, the screengrid voltage V increases in percent to a greater extent, thus aifecting the anode current. In order to eliminate the influence of the screen-grid voltage V the line-deflection circuit shown in FIGURE 5 includes a circuit according to the invention comprising voltage-dependent resistor 7, capacitor 8- and resistor 9. The assembly is supplied by an alternating-voltage source 26 which replaces the alternating-voltage source between tapping 6 and ground in the circuit of FIGURE 1. Capacitor 8 is connected via a separating resistor 27 to voltage-dependent resistor 21 and also via a separate smoothing capacitor 28 to ground. Capacitor 2 8 may be dispensed with if the ripple of the direct voltage V set up across capacit-or 8 is small enough.

As is well-known, the voltage V across capacitor 18, which may be of the order of from 900 to 1000 volts, comprises a portion V which is equal to the voltage across deflection coil 17 during the stroke of the sawtooth current through this coil, and a portion V which is substantially equal to the supply voltage V Consequently, if the voltage V varies due to a variation in the supply voltage, V also varies. The voltage source 26 may be an alternating voltage obtained directly from the AC. supply. Resistor 9 must be chosen so that for the comparatively high voltage V (V =V +V V the positive voltage V across capacitor 8 at the nominal supply voltage V is adjusted to the negatively sloped portion of curve '12 in FIGURE 4.

Also, the positive voltage V requires a value such that it provides, together with the negative voltage developed by means of voltage-dependent resistor 21, a negative control-grid voltage which causes tube 14 just to convey the desired anode current at the nominal supply voltage.

If the supply voltage V increases, then V decreases and hence the resulting negative control-grid voltage for tube v14 increases. The influence of the increasing screengrid voltage V may thus be compensated.

The reverse phenomenon naturally occurs if the supply voltage decreases.

It is possible in this way to stabilize the line-deflection circuit both with regard to variations in the high-voltage load, which is connected to the cathode of diode "19 and 10. A circuit for producing a direct voltage for a load device comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, 21 source of sinusoidal symmetrical alternating voltage, means serially connecting said resistance element and said capacitor with said source of alternating voltage to form a closed current path, a second resistor, a source of direct volt-age, means serially connecting said resistance element and said second resistor with said direct voltage source to form a DC. current path, said circuit being proportioned so that said alternating voltage source produces a net mean alternating current flow in said resistance element which exceeds the DC. current flow therein produced by said direct voltage source whereby a direct voltage is produced across said capacitor.

11. A circuit for producing a regulated direct voltage comprising a resistance element having a non-linear symmetrical current-voltage characteristic, a capacitor, a source of symmetrical alternating voltage adapted to have variations in amplitude, means connecting said resistance element and said capacitor in series circuit with said alternating voltage source to form a junction between said capacitor and said resistance element, a second resistor having a tap point, means producing a direct voltage having an amplitude which varies with amplitude variations of said alternating voltage source, means connecting one end of said second resistor to said junction, means for applying said direct voltage to the series combination of said resistance element and said second resistor, said resistance element and said second resistor being proportioned so that a substantial bias voltage is developed across said resistance element whereby a direct voltage is produced across said capacitor, output circuit means connected across said capacitor and the portion of said second resistor located between said tap point and said junction, said tap point being located to satisfy the following expression:

AVFE wherein AV is an incremental change of said direct voltage and AV is an incremental change in the opposite direction of the direct voltage across said capacitor for a given amplitude variation of said alternating voltage, and R is the portion of said second resistor between the tap point and said junction and R is the remaining resistance portion of said second resistor, whereby a substantially constant direct voltage is produced across said output circuit.

12. A circuit for producing a direct voltage which varies inversely in amplitude with the amplitude of an alternating voltage comprising a resistance element having non-linear symmetrical current-voltage characteristics, a capacitor, a source of a symmetrical alternating voltage adapted to supply a given amplitude range of voltages, means serially connecting said resistance element and capacitor to said source of alternating voltage, means providing a direct voltage to said resistance element of a magnitude to bias said resistance element to operate over the non-linear region of said characteristic curve for said given amplitude range of voltages whereby a direct voltage is produced across said capacitor which varies inversely in amplitude with the amplitude of said alternating voltage, and output circuit means connected across said capacitor.

References Cited by the Examiner UNITED STATES PATENTS 3/1959 Anderson 307-885 3/1959 Putzr-ath 3l527 

12. A CIRCUIT FOR PRODUCING A DIRECT VOLTAGE WHICH VARIES INVERSELY IN AMPLITUDE WITH THE AMPLITUDE OF AN ALTERNATING VOLTAGE COMPRISING A RESISTANCE ELEMENT HAVING NON-LINEAR SYMMETRICAL CURRENT-VOLTAGE CHARACTERISTICS, A CAPACITOR, A SOURCE OF A SYMMETRICAL ALTERNATING VOLTAGE ADAPTED TO SUPPLY A GIVEN AMPLITUDE RANGE OF VOLTAGES, MEANS SERIALLY CONNECTING SAID RESISTANCE ELEMENT AND CAPACITOR TO SAID SOURCE OF ALTERNATING VOLTAGE, MEANS PROVIDING A DIRECT VOLTAGE TO SAID RESISTANCE ELE- 